The present invention relates to pneumatically-controlled hydraulic antivibration supports and to antivibration systems including such supports.
More particularly, the invention relates to a hydraulic antivibration support for interposing between two rigid elements and comprising:
first and second rigid strength members for fixing to the two rigid elements that are to be united;
an elastomer body interconnecting the two strength members and defining part of a liquid-filled working chamber, said elastomer body being adapted to support a static load directed along a central axis;
a flexible elastomer wall forming two adjacent bags which define respectively a compensation chamber and an additional hydraulic chamber, both filled with liquid and connected to the working chamber respectively via a constricted first passage and via a second passage;
a rigid partition extending perpendicularly to the central axis and secured to the second strength member, said rigid partition separating the working chamber from the compensation chamber and from the additional hydraulic chamber;
a rigid protective cup covering the flexible wall and encompassing both the compensation chamber and the additional hydraulic chamber, said protective cup having an end wall and a peripheral side wall fixed to the second strength member; and
a rigid thimble which has an annular side wall extending in the direction of the central axis between a closed end wall and an open end, said thimble being pressed against the flexible wall and clamping said flexible wall in leakproof manner against the rigid partition around the second bag formed in said flexible wall so as to separate the compensation chamber from the additional hydraulic chamber, and said thimble presenting an inside surface which co-operates with said second bag to define a pneumatic chamber communicating with a pneumatic duct.
Document FR-A-2 782 764 describes an example of such an antivibration support, which gives entire satisfaction, particularly concerning attenuation of vibration at the idling frequency of an engine mounted in vehicle bodywork by means of the antivibration support.
Nevertheless, it can be desirable to further improve antivibration supports of this type, in particular to facilitate deformation of the first bag of the flexible wall. In addition, the second bag of the flexible wall of that known support is itself quite rigid and designed specifically to enter into vibration under the effect of alternating pressure rises and falls generated in the pneumatic chamber, but it would be desirable for this second bag to be made more flexible so that it can deform freely solely under the effect of variations in the volume of the working chamber, in particular when the engine is idling if the antivibration support is supporting an engine, so as to avoid the need to control the displacements of said second bag in positive manner.
A particular object of the present invention is to resolve these technical problems.
To this end, the invention provides an antivibration support of the kind in question which is characterized:
in that the additional hydraulic chamber is adjacent to the side wall of the protective cup;
in that the compensation chamber is juxtaposed to said additional hydraulic chamber without surrounding said additional hydraulic chamber, said compensation chamber being in contact with the rigid partition via a first surface area that is more than four times greater than a second surface area of said rigid partition which is in contact with the additional hydraulic chamber; and
in that the thimble extends parallel to the central axis to the end wall of the protective cup, the second bag of the flexible wall extending at rest to the vicinity of the end wall of said thimble.
By means of these dispositions:
the compensation chamber is easily deformable given its one-piece shape and its large volume; and
the additional hydraulic chamber is itself easily deformable, where appropriate solely under the effect of variations in the volume of the working chamber, thus making it possible, where so desired, to avoid positively controlling the displacements of the second flexible bag.
In preferred embodiments of the invention, it is also possible to make use of one or more of the following dispositions:
the rigid partition has a central portion provided with a decoupling valve member formed by a flexible elastomer membrane which separates the working chamber from the compensation chamber and which is adapted to vibrate within limited clearance between these two chambers, the second passage being disposed radially outside said decoupling valve member, and the compensation chamber being disposed substantially to correspond with the decoupling valve member;
the rigid partition has two grids communicating respectively with the working chamber and with the compensation chamber to limit the clearance for the decoupling valve member, the free end of the thimble being placed radially outside the grid which communicates with the compensation chamber, placing a solid portion of said rigid partition;
the second passage is a constricted passage, said first and second throttle passages being dimensioned to present different first and second resonant frequencies respectively, the first resonant frequency being less than 20 hertz (Hz) and the second resonant frequency lying in the range 20 Hz to 80 Hz;
the flexible elastomer wall has a peripheral edge which is clamped in leakproof manner between the side wall of the protective cup and the rigid partition, the open end of the side wall of the thimble being shaped substantially as a circular segment and presenting firstly a curved portion running along the side wall of the protective cup, and secondly a substantially rectilinear portion between the compensation chamber and the additional hydraulic chamber; and
the second passage extends substantially parallel to the central axis.
The invention also provides a motor vehicle comprising:
bodywork supporting an engine via at least one hydraulic antivibration support as defined above;
a three-port valve mounted in the vehicle independently of the antivibration support and adapted to make the pneumatic chamber of the antivibration support communicate either with the atmosphere or with a source of suction; and
a control device mounted in the vehicle independently of the antivibration support and adapted to actuate the three-port valve so as to make the pneumatic chamber of the antivibration support communicate with the atmosphere when the engine of the vehicle is operating at a speed below a predetermined limit, and so as to make the pneumatic chamber of the antivibration support communicate with the source of suction when the vehicle engine is operating at a speed greater than said predetermined limit.
In particular, said predetermined limit can correspond to an engine speed that generates vibration at a frequency that lies in the range 20 Hz to 100 Hz, and that is not less than said second resonant frequency.